The present invention relates to a field distribution measuring method and apparatus for measuring a distribution of an electric field or a magnetic field by a probe sweeping, more specifically, to a field distribution measuring method and apparatus which can eliminate measured noises generated due to offsets between probe sweeping positions and measuring timings.
Small antenna directivity evaluation apparatuses and electromagnetic wave monitoring visualizing apparatuses must measure two-dimensional distributions of electric fields or magnetic fields. These apparatuses have conventionally used a field measurement method in which a probe sweeps two-dimensionally to measure two-dimensional distributions of electric fields or magnetic fields.
The conventional field distribution measuring method and apparatus will be explained with reference to FIG. 6.
A field distribution measurement screen 100 which defines an area in which electric fields or magnetic fields are to be measured includes a probe 102 for detecting electric fields or magnetic fields. The probe 102 is connected to a probe sweep control unit 104 and can sweep in the x-axial direction and the y-axial direction. The probe 102 is connected to a measuring unit 106 which measures electric fields or magnetic fields, based on signals from the probe 102. The probe sweep control unit 104 outputs a measurement trigger signal corresponding to a position of the probe 102 and supplies the measurement trigger signal to the measuring unit 106. Data F of the electric fields or magnetic fields measured by the measuring unit 106 are recorded in a buffer memory 108 together with position information supplied by the probe sweep control unit 104. The buffer memory 108 is connected to a computing/display unit 110 which processes and displays in two-dimensional plane measured data stored in the buffer memory 108.
In the field distribution measuring apparatus shown in FIG. 6, a field distribution is measured by the probe 102 sweeping the field distribution measurement screen 100 while electric fields or magnetic fields being measured on the field distribution measurement screen 100, and measured electric fields or magnetic fields are processed together with position information of the probe 102.
The probe 102 continuously sweeps the field distribution measurement screen 100 without pausing at each sampling point (measuring point) so that the probe 102 can sweep without loss for maximum measurement throughput. As exemplified in FIG. 6, the probe 102 is moved in the positive direction along the x-axis, then moved by a prescribed value in the positive direction along the y-axis, next moved in the negative direction along the x-axis, then moved by a prescribed value in the positive direction along the y-axis, and then moved in the positive direction along the x-axis. The probe 102 repeats these motions so as to sweep substantially all the surface of the field distribution measurement screen 100 (hereinafter call such sweep xe2x80x9czigzag sweepxe2x80x9d).
The probe sweep control unit 104 outputs measurement trigger signals corresponding to positions of the probe 102 while the probe 102 is sweeping the field distribution measurement screen 100. As exemplified in FIG. 7, a plurality of x coordinates are set in advance, spaced equidistantly from each other along the x-axis, and when an x coordinate of a position of the probe 102 comes to each of the set x-coordinates, the probe sweep control unit 104 outputs a measurement trigger signal. The measurement trigger signals are supplied to the measuring unit 106.
The measuring unit 106 judges a signal detected by the probe 102 when the measuring unit 106 received the measurement trigger signal to be information of electric fields or magnetic fields, and measures the electric fields or magnetic fields, based on the signal outputted by the probe 102.
Data of electric fields or magnetic fields thus measured are stored by the buffer memory 108 together with position information (coordinates (x,y)) of the probe outputted by the prove sweep control unit.
Next, the data stored by the buffer memory 108 are developed on a two-dimensional plane by the computing/display unit 110, and a two-dimensional field distribution of electric fields or magnetic fields can be displayed.
However, there is a delay time from detection of a measurement trigger signal to output of a measured value. Accordingly, in the conventional field distribution measuring method described above, in which the probe continuously sweeps without pausing at each sampling position for higher measuring throughputs, an x coordinate of the probe 102 at the time of outputting a measurement trigger signal is displaced from an x coordinate of the probe 102 at the time of the actual measurement.
Furthermore, as shown in FIG. 7, when the probe 102 sweeps zigzag, the shift of coordinates on an odd number-th line on the y-axis and that of coordinates on an even number-th line on the y-axis take place in directions opposite to each other. That is, on an odd number-th line on the y-axis, where the probe is moved along the x-axis in the positive direction, sampling points shift in the positive direction (circled in FIG. 7). Oppositely, on an even number-th line on the y-axis, where the probe is moved along the x-axis in the negative direction, sampling points shift in the negative direction (crossed in FIG. 7). A deviation amount of the sampling points between the odd number-th line and the even number-th line is 2xvxtdd [m] by which x axial sampling positions on both lines deviates from each other for the same trigger point when a sweeping velocity of the probe is v [m/s], and a delay time is td [see].
Accordingly, by developing a field distribution on a two-dimensional plane, based on the position information outputted by the probe sweep control unit 104, correct two-dimensional images of electric fields or magnetic fields cannot be obtained.
An object of the present invention is to provide a field distribution measuring method and apparatus for measuring a distribution of electric fields or magnetic fields by continuously sweeping a probe, wherein measuring noises generated due to offsets between sweeping positions of the probe and measuring timings can be removed.
The above-described object can be achieved by a field distribution measuring method for measuring an electric field or a magnetic field by a probe measuring at a plurality of sampling points while continuously sweeping, wherein a shift amount of the sampling points is computed, based on a spurious spectrum generated by a displacement between a position of the probe and a measuring timing, and a distribution of the electric field or the magnetic field is measured in consideration of the shift amount.
In the above-described field distribution measuring method, it is possible that the method comprises the steps of: storing a plurality of measured data obtained by the probe sweeping in a first direction together with position information of the probe as reference data; storing a plurality of measured data obtained by the probe sweeping in a second direction opposite to the first direction together with position information of the probe as adjustment data; interpolating the adjustment data to compute interpolated data with data between the sampling points interpolated; computing spatial frequency power spectra for the reference data and the interpolated data; and computing the shift amount of the sampling points, based on the spatial frequency power spectra.
In the above-described field distribution measuring method, it is possible that the shift amount of the sampling points is computed based on an accumulated value of the spatial frequency power spectra.
In the above-described field distribution measuring method, it is possible that the shift amount of the sampling points is judged, based on a point where the accumulated value of the spatial frequency power spectra is below a prescribed value.
In the above-described field distribution measuring method, it is possible that the shift amount of the sampling points is judged, based on a point where the accumulated value of the spatial frequency power spectra is minimum.
In the above-described field distribution measuring method, it is possible that the shift amount of the sampling points is computed in consideration of acceleration and deceleration of the probe.
In the above-described field distribution measuring method, it is possible that the probe sweeps on a two-dimensional plane.
In the above-described field distribution measuring method, it is possible that the probe sweep in a three-dimensional space.
The above-described object can be also achieved by a field distribution measuring apparatus comprising: a probe for detecting an electric field or a magnetic field at a plurality of sampling points while continuously sweeping on a plane or in a space; a measuring unit for measuring the electric field or the magnetic field detected by the probe; a storing unit for storing data of the electric field or the magnetic field measured by the measuring unit together with position data of the probe; a data processing unit for computing a shift amount of sampling points generated by a displacement between a position of the probe and a measuring timing, based on data stored in the storing unit; and a computing unit for computing a spatial distribution of the electric field or the magnetic field detected by the probe, in consideration of the shift amount of the sampling points computed by the data processing unit.
In the above-described field distribution measuring apparatus, it is possible that the data processing unit computes the shift amount of the sampling points, based on a spurious spectrum generated by the displacement between the position of the probe and the measuring timing.
According to the present invention, a field distribution measuring method for measuring a spatial distribution of an electric field or a magnetic field at a plurality of sampling points by the probe continuously sweeping the sampling points, in which, based on spurious spectra generated by offsets between positions of the probe and measuring timings, a shift amount of the sampling points is computed, and, taking into account the shift amount, a distribution of electric fields or magnetic fields is measured. Thus, measured noises generated due to offsets between sweeping positions of the probe and measuring timings can be properly removed.